1. Field of the Invention
The present invention relates to an ink jet head block of the so-called "on-demand type" for printing by ejecting ink droplets from nozzles.
2. Description of the Prior Art
The ink jet head of the on-demand type of the prior art is exemplified in Japanese Patent Laid-Open 14261/1980 (i.e., Prior Art 1) and Japanese Patent Publication No. 4309/1984 (i.e., Prior Art 2) by a structure, in which ink passages are arranged generally in parallel at the end face of the nozzle to have their one-side ends arrayed at the central portion and are individually equipped at their individual end portions at the central portion with nozzles extending through a passage substrate so that ink droplets may fly perpendicularly of the ink passages.
In the Prior Art 1, all the ink passages have their outer circumferential end portions communicating with a common ink chamber so as to supply the ink to the ink passages, and the ink supply holes are projected outward from a portion of the common ink chamber. However, there is no disclosure on the structure for supplying the ink to the ink supply holes and the means for supplying an electric power to the piezoelectric elements in a pressure chamber disposed in the ink passages.
In the Prior Art 2, the ink passages are formed separately in a plurality of layers to densify the nozzles highly. The ink supply passages are projected backward, but there is no disclosure on the structure for supplying the ink to the ink supply passages and the means for pressurizing and ejecting the ink in the ink supply passages.
In the Prior Art 1, the ink supply holes are projected outward. In order to supply these ink supply holes with the ink, the common ink chamber has to be arranged outside of the ink supply holes so that the space is two-dimensionally enlarged. In addition, the assembly cannot be made merely by stacking so that it is not suitable for automation.
In the Prior Art 2, the individual ink supply passages are projected backward and have to be supplied with the ink. As a result, the space is enlarged not in the two-dimensional directions but in the thickness direction. Moreover, the ink supply passages require means for communicating with the ink tank so that the structure is complicated. Like the aforementioned example, the assembly cannot be made merely by the stacking so that it is not suitable for automation.